Is there any benefit to the WSM over regular belted mags?

It depends on your needs. I don't own 30 calibers but do know this. From a pure accuracy standpoint, there is an advantage in a shorter case. It has been proven over the past 50 years of bench rest shooting. Certainly long cases can be very accurate and win matches. No one will argue that. Day in and day out though, the shorter powder column with it's more consistant ignition will be inherently more accurate. For hunting purposes, the wsm's have a modest powder capacity compred to the big boys. This extra capacity is nice when you want to launch heavy, high bc bullets at top velocities. That's my take on it anyhow.

What is the shoulder angle? Who made the dies and reamers? I heard somewhere that Lapua is making(coming up with) a factory chambering 30/338 Lapua. Is that true? Sounds really nice for a switch barrel if you already have a 338 Lapua. Thank you